Systems and methods for enhanced mimo operation

ABSTRACT

A method for channel state information (CSI) reporting by a wireless communication device is described. The method includes determining a codebook for a CSI report corresponding to four transmit antenna (4Tx) transmissions from a base station. The codebook has a dual codebook structure. The method also includes generating the CSI report using the codebook. The method further includes transmitting the CSI report to a base station.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/199,743, filed Mar. 6, 2014, for “SYSTEMS AND METHODS FOR ENHANCEDMIMO OPERATION,” which claims priority from U.S. Provisional PatentApplication Ser. No. 61/775,016, filed Mar. 8, 2013, for “CODEBOOKDESIGN AND CSI FEEDBACK FOR ENHANCED MIMO OPERATION IN LTE,” U.S.Provisional Patent Application Ser. No. 61/821,867, filed May 10, 2013,for “CODEBOOK DESIGN AND CSI FEEDBACK FOR ENHANCED MIMO OPERATION INLTE,” and U.S. Provisional Patent Application Ser. No. 61/832,310, filedJun. 7, 2013, for “CODEBOOK DESIGN AND CSI FEEDBACK FOR ENHANCED MIMOOPERATION IN LTE.”

TECHNICAL FIELD

The present disclosure relates generally to wireless communicationsystems. More specifically, the present disclosure relates to systemsand methods for codebook design and channel state information (CSI)feedback for enhanced multiple-input and multiple-output (MIMO)operation in Long Term Evolution (LTE).

BACKGROUND

Wireless communication systems are widely deployed to provide varioustypes of communication content such as voice, video, data, and so on.These systems may be multiple-access systems capable of supportingsimultaneous communication of one or more wireless communication deviceswith one or more base stations.

A problem that must be dealt with in all communication systems isinterference. There may be problems with decoding the signals received.In wireless communication, one way to deal with these problems is byutilizing channel state information (CSI) feedback. As part of channelstate information (CSI) feedback, a wireless communication device maysend channel quality indicator (CQI) values to one or more basestations. The one or more base stations may use the channel qualityindicator (CQI) values to schedule wireless transmissions.

The use of codebooks allows a wireless communication device to indicateto a base station the format of channel state information (CSI)feedback. Different codebooks can provide different benefits. Forexample, some codebooks provide increased payloads, some provide highfeedback accuracy and some codebooks provide low overhead. Benefits maybe realized by using adaptive codebooks for channel state information(CSI) feedback.

SUMMARY

A method for channel state information (CSI) reporting is described. Themethod includes determining a codebook for a CSI report corresponding tofour transmit antenna (4Tx) transmissions from a base station. Thecodebook has a dual codebook structure. The method also includesgenerating the CSI report using the codebook. The method furtherincludes transmitting the CSI report to a base station.

The dual codebook structure may be a block-diagonal grid of beamsstructure. A first matrix may define a grid of beams for eachpolarization. A second matrix may perform beam selection within a beamgroup and co-phasing.

The codebook may be determined based on at least one of a grid of beamresolution, a size of the beam groups, an overlap between beam groups,and a co-phasing accuracy. Each of the parameters may be individuallyadaptable to form the codebook.

The method may also include signaling the codebook using signaling basedon at least one of explicit bits, dynamic parameters and semi-staticparameters. New reporting types may be defined to adjust the number ofbits spent for a precoding matrix indicator (PMI) or a channel qualityindicator (CQI) in various reporting modes.

The method may be performed by a wireless communication device. Thewireless communication device may determine which of multiple configuredcodebooks should be used for CSI reporting.

Multiple user channel quality indicator hypotheses may remain separatefrom codebook adaptation. Multiple user channel quality indicatorhypotheses may follow codebook adaptation. The method may also includeperforming codebook subsampling to meet an 11 bit payload constraint forthe CSI report.

A method for CSI reporting by a base station is also described. Themethod includes determining a codebook used by a wireless communicationdevice for a CSI report corresponding to 4Tx transmissions from the basestation. The codebook has a dual codebook structure. The method alsoincludes receiving the CSI report. The method further includes decodingthe CSI report using the codebook.

A wireless communication device for CSI reporting is also described. Thewireless communication device includes a processor, memory in electroniccommunication with the processor and instructions stored in the memory.The wireless communication device determines a codebook for a CSI reportcorresponding to 4Tx transmissions from a base station. The codebook hasa dual codebook structure. The wireless communication device generatesthe CSI report using the codebook. The wireless communication devicetransmits the CSI report to a base station.

A base station for CSI reporting is also described. The base stationincludes a processor, memory in electronic communication with theprocessor and instructions stored in the memory. The base stationdetermines a codebook used by a wireless communication device for a CSIreport corresponding to 4Tx transmissions from the base station. Thecodebook has a dual codebook structure. The base station receives theCSI report. The base station decodes the CSI report using the codebook.

A wireless communication device for CSI reporting is also described. Thewireless communication device includes means for determining a codebookfor a CSI report corresponding to 4Tx transmissions from a base station.The codebook has a dual codebook structure. The wireless communicationdevice also includes means for generating the CSI report using thecodebook. The wireless communication device further includes means fortransmitting the CSI report to a base station.

A base station for CSI reporting is also described. The base stationincludes means for determining a codebook used by a wirelesscommunication device for a CSI report corresponding to 4Tx transmissionsfrom the base station. The codebook has a dual codebook structure. Thebase station also includes means for receiving the CSI report. The basestation further includes means for decoding the CSI report using thecodebook.

A computer-program product for CSI reporting is also described. Thecomputer-program product includes a non-transitory computer-readablemedium having instructions thereon. The instructions include code forcausing a wireless communication device to determine a codebook for aCSI report corresponding to 4Tx transmissions from a base station. Thecodebook has a dual codebook structure. The instructions also includecode for causing the wireless communication device to generate the CSIreport using the codebook. The instructions further include code forcausing the wireless communication device to transmit the CSI report toa base station.

A computer-program product for CSI reporting is also described. Thecomputer-program product includes a non-transitory computer-readablemedium having instructions thereon. The instructions include code forcausing a base station to determine a codebook used by a wirelesscommunication device for a CSI report corresponding to 4Tx transmissionsfrom the base station. The codebook has a dual codebook structure. Theinstructions also include code for causing the base station to receivethe CSI report. The instructions further include code for causing thebase station to decode the CSI report using the codebook.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless communication system with multiple wirelessdevices in which systems and methods for enhanced MIMO operation may beperformed;

FIG. 2 is a block diagram illustrating a radio network operating inaccordance with the systems and methods disclosed herein;

FIG. 3 is a flow diagram of a method for CSI reporting using codebookadaptation;

FIG. 4 is a flow diagram of a method for obtaining CSI reporting usingcodebook adaptation;

FIG. 5 is a flow diagram of a method for periodic CSI reporting usingcodebook adaptation;

FIG. 6 is a block diagram of a transmitter and receiver in a MIMOsystem;

FIG. 7 illustrates certain components that may be included within awireless communication device; and

FIG. 8 illustrates certain components that may be included within a basestation.

DETAILED DESCRIPTION

The 3^(rd) Generation Partnership Project (3GPP) is a collaborationbetween groups of telecommunications associations that aims to define aglobally applicable 3^(rd) generation (3G) mobile phone specification.3GPP Long Term Evolution (LTE) is a 3GPP project aimed at improving theUniversal Mobile Telecommunications System (UMTS) mobile phone standard.The 3GPP may define specifications for the next generation of mobilenetworks, mobile systems and mobile devices. In 3GPP LTE, a mobilestation or device may be referred to as a “user equipment” (UE).

The systems and methods disclosed herein may be described with referenceto one or more specifications, such as 3GPP Release-8, 3GPP Release-9,3GPP Release-10, 3GPP Release-11, 3GPP Release-12, LTE and Long TermEvolution Advanced (LTE-A). However, the concepts may also be applied toother wireless communication systems.

Various configurations are now described with reference to the Figures,where like reference numbers may indicate functionally similar elements.The systems and methods as generally described and illustrated in theFigures herein could be arranged and designed in a wide variety ofdifferent configurations. Thus, the following more detailed descriptionof several configurations, as represented in the Figures, is notintended to limit scope, as claimed, but is merely representative of thesystems and methods.

FIG. 1 shows a wireless communication system 100 with multiple wirelessdevices in which systems and methods for enhanced MIMO operation may beperformed. Wireless communication systems 100 are widely deployed toprovide various types of communication content such as voice, data, andso on. A wireless device may be a wireless communication device 104 or abase station 102. Both the wireless communication device 104 and thebase station 102 may be configured to use a multiple codebook 108procedure.

A base station 102 is a station that communicates with one or morewireless communication devices 104. A base station 102 may also bereferred to as, and may include some or all of the functionality of, anaccess point, a broadcast transmitter, a NodeB, an evolved NodeB, etc.The term “base station” will be used herein. Each base station 102provides communication coverage for a particular geographic area. A basestation 102 may provide communication coverage for one or more wirelesscommunication devices 104. The term “cell” can refer to a base station102 and/or its coverage area depending on the context in which the termis used.

A wireless communication device 104 may also be referred to as, and mayinclude some or all of the functionality of, a terminal, an accessterminal, a user equipment (UE), a subscriber unit, a station, etc. Awireless communication device 104 may be a cellular phone, a personaldigital assistant (PDA), a wireless device, a wireless modem, a handhelddevice, a laptop computer, etc.

Communications in a wireless system (e.g., a multiple-access system) maybe achieved through transmissions over a wireless link. Such acommunication link may be established via a single-input andsingle-output (SISO), multiple-input and single-output (MISO),multiple-input and multiple-output (MIMO), or a coordinated multipoint(CoMP) system. A MIMO system includes transmitter(s) and receiver(s)equipped, respectively, with multiple (NT) transmit antennas andmultiple (NR) receive antennas for data transmission. SISO and MISOsystems are particular instances of a MIMO system. The MIMO system canprovide improved performance (e.g., higher throughput, greater capacityor improved reliability) if the additional dimensionalities created bythe multiple transmit and receive antennas are utilized.

The wireless communication system 100 may utilize MIMO. A MIMO systemmay support both time division duplex (TDD) and frequency divisionduplex (FDD) systems. In a TDD system, uplink 126 and downlink 124transmissions are on the same frequency region so that the reciprocityprinciple allows the estimation of the downlink 124 channel from theuplink 126 channel. This enables a transmitting wireless device toextract transmit beamforming gain from communications received by thetransmitting wireless device.

The wireless communication system 100 may be a multiple-access systemcapable of supporting communication with multiple wireless communicationdevices 104 by sharing the available system resources (e.g., bandwidthand transmit power). Examples of such multiple-access systems includecode division multiple access (CDMA) systems, wideband code divisionmultiple access (W-CDMA) systems, time division multiple access (TDMA)systems, frequency division multiple access (FDMA) systems, orthogonalfrequency division multiple access (OFDMA) systems, single-carrierfrequency division multiple access (SC-FDMA) systems, 3^(rd) GenerationPartnership Project (3GPP) Long Term Evolution (LTE) systems and spatialdivision multiple access (SDMA) systems.

The terms “networks” and “systems” are often used interchangeably. ACDMA network may implement a radio technology such as UniversalTerrestrial Radio Access (UTRA), cdma2000, etc. UTRA includes W-CDMA andLow Chip Rate (LCR) while cdma2000 covers IS-2000, IS-95 and IS-856standards. A TDMA network may implement a radio technology such asGlobal System for Mobile Communications (GSM). An OFDMA network mayimplement a radio technology such as Evolved UTRA (E-UTRA), IEEE 802.11,IEEE 802.16, IEEE 802.20, Flash-OFDMA, etc. UTRA, E-UTRA, and GSM arepart of Universal Mobile Telecommunication System (UMTS). Long TermEvolution (LTE) is a release of UMTS that uses E-UTRA. UTRA, E-UTRA,GSM, UMTS and LTE are described in documents from an organization named“3rd Generation Partnership Project” (3GPP). cdma2000 is described indocuments from an organization named “3rd Generation Partnership Project2” (3GPP2). For clarity, certain aspects of the techniques are describedbelow for LTE, and LTE terminology is used in much of the descriptionbelow.

A wireless communication device 104 may communicate with zero, one, ormultiple base stations 102 on the downlink 124 and/or uplink 126 at anygiven moment. Multiple channels may be used between a base station 102and a wireless communication device 104 on both the downlink 124 and theuplink 126. A physical uplink shared channel (PUSCH) may be used totransmit user data from a wireless communication device 104 to a basestation 102. A physical uplink control channel (PUCCH) may be used totransport user signaling data from a wireless communication device 104to a base station 102. A physical downlink shared channel (PDSCH) may beused to transmit common user data and control information from a basestation 102 to a wireless communication device 104. A physical downlinkcontrol channel (PDCCH) may be used to transmit control information froma base station 102 to a wireless communication device 104.

Based on communications received from one or more base stations 102, awireless communication device 104 may generate one or more types ofchannel state information (CSI), such as channel quality indicators(CQIs), precoding matrix indicators (PMIs) and rank indicators (RIs).Each channel quality indicator (CQI) may be associated with a channelmeasurement for the downlink 124 channel between the base station 102and the wireless communication device 104. Each channel qualityindicator (CQI) may be conditioned on certain interference assumptions.A channel quality indicator (CQI) may be dependent on the transmissionscheme used in the wireless communications system.

A wireless communication device 104 may use the CSI feedback informationto determine a preferred beam. A preferred beam may refer to the antennastructure, weight, transmission direction and phase of a signaltransmitted by a base station 102 to the wireless communication device104. The terms “beam” and “precoding vector” may refer to the directionin which data is streamed wirelessly from an antenna. In multiple-inputand multiple-output (MIMO), multiple beams may be used to transmitinformation between a base station 102 and a wireless communicationdevice 104. A preferred beam may thus refer to a beam that produces thebest (i.e., the optimal) data stream between the base station 102 andthe wireless communication device 104.

Multi-user multiple-input and multiple-output (MU-MIMO) may increaseuser throughputs on the downlink 124 over traditional single-usermultiple-input and multiple-output (SU-MIMO) by making more intelligentuse of the base station 102 resources. Multi-user multiple-input andmultiple-output (MU-MIMO) may enable an increase in throughput for aparticular transmission time interval (TTI) compared with dual-streamtransmission to a single wireless communication device 104. A basestation 102 may thus determine whether to use dual downlink 124 datastreams for a single wireless communication device 104 (i.e., SU-MIMO)or to use a first data stream for a first wireless communication device104 and a second data stream (e.g., orthogonal to the first data stream)for a second wireless communication device 104 (i.e., multi-usermultiple-input and multiple-output (MU-MIMO)).

The CSI feedback information may correspond to a request for asingle-stream transmission or a dual-stream transmission. For example, awireless communication device 104 may include multiple channel qualityindicators (CQIs). The wireless communication device 104 may generatemultiple channel quality indicators (CQIs) for each transmission timeinterval (TTI). A wireless communication device 104 may not send everychannel quality indicator (CQI) to the base station 102 for everytransmission time interval (TTI). In some configurations, a wirelesscommunication device 104 may send only the optimal channel qualityindicator (CQI) to the base station 102 for each transmission timeinterval (TTI).

If the wireless communication device 104 determines that it has goodgeometry with respect to the base station 102 (e.g., the channel qualitybetween the base station 102 and the wireless communication device 104is above a threshold), the wireless communication device 104 may send anoptimal dual-stream multiple-input and multiple-output (MIMO) channelquality indicator (CQI) to the base station 102. If the wirelesscommunication device 104 determines that it has bad geometry withrespect to the base station 102 (e.g., the channel quality between thebase station 102 and the wireless communication device 104 is below thethreshold), the wireless communication device 104 may send an optimalsingle-stream multiple-input and multiple-output (MIMO) channel qualityindicator (CQI) to the base station 102.

The wireless communication device 104 may include a CSI report transmitmodule 106. The CSI report transmit module 106 may generate CSI reports132 and transmit these CSI reports 132 to the base station 102. Sincethese CSI reports 132 provide the base station 102 with informationabout the downlink 124 channel from the base station 102 to the wirelesscommunication device 104 using MIMO, these CSI reports 132 may bereferred to as DL MIMO CSI feedback. DL MIMO CSI feedback may bereported periodically or aperiodically.

The wireless communication device 104 may use a codebook 108 a (a set ofpre-agreed parameters) for each CSI report 132. The codebook 108 a mayinstruct the base station 102 on how to interpret a received CSI report132, including what information is included in the CSI report 132 andthe formatting of the CSI report 132.

The codebook 108 may have different structures depending on the numbertransmit antennas that are used by the base station 102. The codebook108 structure for 8Tx (i.e., eight transmit antennas used by the basestation 102) has been defined. This codebook 108 structure defines adual codebook 108 structure tailored to cross-polarized (X-pol) antennastructures. This structure is motivated by a preference from operatorsand by the large form factor of 8Tx-ULA (uniform linear array).

The codebook 108 structure for 8Tx defines a block diagonal grid ofbeams (GoB) structure W=W₁·W₂. In one configuration, W₁ may correspondto properties for a long-term and/or wideband channel and W₂ maycorrespond to properties for a short-term and/or narrowband channel.

In the GoB structure, the W₁ matrix 118 is an 8×2N_(b) matrix defined as

$W_{1} = {\begin{bmatrix}X & 0 \\0 & X\end{bmatrix}.}$

Within the W₁ matrix 118, X is a 4×N_(b) matrix defining the GoB foreach polarization. N_(b) represents the number of beams within a beamgroup. Since the W₁ matrix 118 is reported only for wideband, havingmultiple overlapping beam groups per W₁ matrix 118 allows the W₂ matrix120 to select among the optimal beams within the beam group on aper-subband basis. The W₂ matrix 120 is a 2N_(b)×r matrix. The W₂ matrix120 performs beam selection within the beam group and co-phasing. In W₂,r denotes the selected transmission rank.

However, a dual codebook 108 structure that includes the W₁ matrix 118and the W₂ matrix 120 (as are used in the 8Tx case) has not been definedfor 4Tx (i.e., four transmit antennas used by the base station 102). Inone configuration, the codebook 108 structure for 4Tx may retain theblock-diagonal GoB structure that has been defined for 8Tx. Thus, the W₁matrix 118 may be a 4×2N_(b) matrix defined as

$W_{1} = {\begin{bmatrix}X & 0 \\0 & X\end{bmatrix}.}$

Within the W₁ matrix 118, X may be a 2×N_(b) matrix defining the GoB foreach polarization. The W₂ matrix 120 may be a 2N_(b)×r matrix. Thebenefits of using the same block-diagonal GoB structure for 4Tx as isused for 8Tx is that the codebook 108 structure remains tailored toX-pol deployments, which are an important scenario in practice.Additionally, overlapping beam groups have the benefit that a single W₁matrix 118 can be optimal across the entire system bandwidth (overlapavoids edge effect).

A dual codebook 108 that includes the W₁ matrix 118 and the W₂ matrix120 may be defined as a function of one or more parameters. Theseparameters may include the GoB resolution 110, the size of the beamgroups 112, the overlap between beam groups 114 and the co-phasingaccuracy 116 (e.g., the impact of the W₂ payload).

When selecting a codebook 108 (and the parameters used for the codebook108), two tradeoffs should be considered. The first tradeoff is generalaccuracy vs. feedback overhead. The computation aspects of the wirelesscommunication device 104 also need to be considered. The second tradeoffis a W₁ vs. W₂ payload tradeoff. W₁ is reported wideband but W₂ isreported subband.

The parameters used for generating the codebook 108 should bereconsidered when going from 8Tx to 4Tx. By using an adaptable codebook108, each of the parameters in the codebook 108 can be configuredindependently (referred to herein as codebook adaptation). Codebookadaptation avoids having to compromise across different antennaconfigurations and/or channel conditions (e.g., line of sight (LoS) vs.non-line of sight (NLoS)). Codebook adaptation may involve any of theparameters in the codebook 108 (i.e., the GoB resolution 110, the sizeof beam groups 112, the overlap between beam groups 114 and theco-phasing accuracy 116). Codebook adaptation may also include theselection of codebooks 108 with different structures (e.g., legacy 4Txcodebooks 108) for which the aforementioned parameters may not berelevant.

Design alternatives for codebook 108 parameter optimization are givenbelow in Table 1 (however, other parameter combinations may also beconsidered):

TABLE 1 Codebook Parameter Design Alternatives GoB Resolution 64 32 1616 16 8 Number of beam groups 32 16 8 16 16 8 Number of beams within 4 44 2 1 1 each beam group Overlap between beam 2 2 2 1 0 0 groups Numberof Co-phasing 4 4 4 4 4 4 choices (W₂) W₁ payload 5 bit 4 bit 3 bit 4bit 4 bit 3 bit W₂ payload 4 bit 4 bit 4 bit 3 bit 2 bit 2 bit

In one example, codebook adaptation may support two parameter sets: oneparameter set may be tailored to high feedback accuracy and oneparameter set may be tailored to low overhead. Codebook adaptation mayalso consider switching between the legacy Rel-8 Householder (HH)codebook 108 and the enhanced dual codebook 108 according to the systemsand methods described herein. The Rel-8 codebook 108 may be sufficientfor rank-3 and rank-4 operation. In this case, it may be desirable toreport the precoding matrix only on wideband to reduce the feedbackoverhead for higher ranks.

As discussed above, the block diagonal GoB structure W=W1·W2 may be usedfor a dual codebook 108 structure for 4Tx. Thus, the CSI report 132 mayinclude indices corresponding to a W₁ matrix 118 and a W₂ matrix 120,respectively. The CSI report 132 may be provided to a base station 102.The base station 102 may include a CSI report decode module 122. The CSIreport decode module 122 may be used by the base station 102 to receivea CSI report 132 and decode the CSI report 132 using the appropriatecodebook 108 b. In some configurations, the CSI report decode module 122may also signal to the wireless communication device 104 which codebook108 b the wireless communication device 104 is to use.

In one configuration, the codebooks 108 b may be explicitly defined. Forexample, the specification may include a listing of each codebook 108explicitly. One or more codebooks 108 may be defined, allowing forcodebook adaptation. In other words, the codebook 108 parameters may bedefined explicitly.

In another configuration, the codebook 108 parameters may be signaledexplicitly (rather than using preset codebooks 108). The set ofparameters corresponding to the codebook 108 may be defined and thesedefined parameters may be signaled (e.g., through RRC signaling) foreach codebook 108. This allows greater flexibility, as presumably anycombination of codebook 108 parameters could be allowed. However, thishas the drawback of increased wireless communication device 104complexity of managing a potentially greater number of codebooks 108.Some parameter combinations could be reserved and associated withpredefined codebook 108 structures. For example, the legacy 4Tx Rel-8LTE codebook 108 may be used.

In transmission mode 10 (TM10), multiple CSI processes are supported.Each CSI process may correspond to specific channel and interferencehypotheses. Multiple signaling options may be considered. In a firstsignaling option, the codebook 108 may be common across all configuredCSI processes. This is simple but inflexible. In a second signalingoption, a single codebook 108 can be configured for each CSI process.The configuration of a codebook 108 per CSI process enables the networkto report CSI for different transmission points with different accuracylevels. This scalable feedback may be beneficial, since differenttradeoffs in terms of CSI accuracy vs. uplink 126 overhead may beachievable.

In a third signaling option, one or more codebooks 108 can be configuredfor each CSI process. This allows for dynamic selection of one codebook108 among the configured codebooks 108. The codebook 108 may be signaledusing dynamic signaling based on explicit bits, implicit signaling basedon dynamic parameters or implicit signaling based on semi-staticparameters.

For dynamic signaling based on explicit bits, new bits may be defined inthe downlink control information (DCI) to signal which of the one ormore codebooks 108 should be selected. Existing but unused code points(defined by the existing DCI bits) may also be used equivalently. Someform of broadcast signaling may also be used. The use of broadcastsignaling is motivated by the fact that it may be beneficial formultiple wireless communication devices 104 to use the same codebook 108(e.g., for improved multiple user multiple-input and multiple-output(MU-MIMO) operation). It also may be beneficial to switch a large numberof wireless communication devices 104 at the same time. Broadcastsignaling may save signaling overhead.

For implicit signaling based on dynamic parameters, the entries in thesets identifying which CSI process to report upon receiving a specificCSI request field (i.e., the sets linked to the aperiodic CSI triggeringtable) may be amended to identify which CSI process to report and whichcodebook 108 to use. The codebook 108 selected may be associated withone or more parameters: a subframe subset associated with the CSI report132 and/or parameters of the DCI triggering the report (e.g., receivedon common or wireless communication device-specific search space,received through legacy PDCCH or an enhanced PDCCH (EPDCCH)).

For implicit signaling based on semi-static parameters, differentcodebooks 108 may be used for periodic vs. aperiodic reporting of a CSIprocess. For example, a high-accuracy codebook 108 may be used foraperiodic reporting while a low granularity codebook 108 may be used forperiodic reporting. Selection of a specific codebook 108 may also betied to the periodic/aperiodic reporting mode.

The use of codebook adaptation may lead to variable uplink 126 overhead,which may be taken into account as part of encoding/reporting details onthe uplink 126. In the case of aperiodic feedback, the encoding of PMIand CQI can follow the same concatenation rules as used in Rel-11. Inthis case, the network is aware of the codebook 108 used and can decodethe received CSI report 132 without issues.

For periodic CSI feedback, new reporting types may be defined to adjustthe number of bits spent for PMI and/or CQI in various reporting modes.If separate reporting types for each codebook 108 are not defined,additional steps may be taken. For example, if the PMI and/or the CQIbit-width is smaller than the corresponding reporting type, zero-paddingmay be performed. The location of zeros may be known to the network; thenetwork may use the location of zeros as a form of virtual cyclicredundancy check (CRC). By not defining separate reporting types foreach codebook 108, fewer reporting types need to be defined, which is anadded benefit. Periodic CSI feedback and reporting types are discussedin more detail in connection with FIG. 5.

The wireless communication device 104 may provide assistance in helpingthe network determine which codebook 108 should be selected/configured.If codebook adaptation is supported per CSI processes, multiple CSIprocesses can be configured for the wireless communication device 104.The multiple CSI processes may have the same channel and interferenceconfiguration, but different codebook 108 configurations. In oneconfiguration, the wireless communication device 104 may generate a CSIreport 132 for each codebook 108. The network may receive the CSIreports 132 for each codebook 108 and then determine which codebook 108is better suited for CSI reporting. This may be transparent to thewireless communication device 104.

In one configuration, the wireless communication device 104 maydetermine which of multiple configured (i.e., candidate) codebooks 108should be used for CSI reporting. The wireless communication device 104may inform the network of the selected codebook 108 through some form ofcodebook type indicator (CTI). The wireless communication device 104 maydetermine the codebook 108 to select, at least in part, based ondownlink 124 vs. uplink 126 traffic characteristics (e.g., is thedownlink 124 gain worth the additional uplink 126 overhead?), batterysaving considerations (e.g., how is the battery life affected by havinglarge/small uplink 126 overhead?), channel statistics (e.g., how doesfrequency/time selectivity of the channel impact anticipated CSIfeedback accuracy?), and quantization accuracy (e.g., does one codebook108 lead to much smaller quantization error than another?). The networkmay also provide signaling or other assistance to help the wirelesscommunication device 104 in making the codebook 108 selection.

Multiple user CQI (MU-CQI) feedback may be performed with Rel-8 4Txcodebooks 108. Wideband MU-CQI offsets may be computed under a set ofhypotheses for a co-scheduled layer. For example, each hypothesis can beassociated with a rank-1 precoder in the codebook 108. Differenthypotheses may be considered and the co-scheduled precoder may beobtained, at least in part, based on the selected PMI of the desiredlayer. The number of different hypotheses and the number of co-scheduledprecoders that are obtained may be represented by the value K. Thedesired layer and the MU-MIMO related information is given for differentranks in Table 2 below:

TABLE 2 RI = 1 RI = 2 Desired Layer PMI (wb; rank-1) PMI (wb; rank-2)SU-CQI (sb; rank-1) SU-CQI (sb; rank-2) MU-MIMO-related MU-CQI offsets(wb) for PMI (wb; rank-1) information the set of K co-scheduled SU-CQI(wb; rank-1) PMIs MU-CQI offsets (wb) for the set of K co-scheduled PMIs

In Table 2, “SU-CQI” represents a single-user channel quality indicator.Furthermore, “wb” represents information that is reported wideband, and“sb” represents information that is reported subband.

MU-CQI feedback may be configured in addition to codebook adaptation. Inone configuration, the MU-CQI hypotheses may remain separate from thecodebook adaptation. Thus, the codebook 108 used to emulate co-scheduledlayers (of other wireless communication devices 104) may use a fixedcodebook 108, which may be different from the codebook 108 that thewireless communication device 104 uses for CSI feedback. In anotherconfiguration, the MU-CQI hypotheses may follow the codebook adaptationdescribed herein. Thus, a set of MU-CQI hypotheses may be defined foreach codebook 108. When the wireless communication device 104 switchescodebooks 108, the wireless communication device 104 may also switchassumptions on how the MU-CQI hypotheses are defined.

The MU-CQI hypotheses may be defined based on the W₁ matrix 118selection only. It may not be necessary to have separate hypotheses fordifferent W₂ matrices 120 associated with the same W₁ matrix 118. Thisresults in a smaller number of hypotheses that need to be considered.The co-scheduled W₁ matrix 118, which is used for MU-CQI computation,may be selected, at least in part, based on the W₁ matrix 118 determinedfor the desired layer of the wireless communication device 104. Forexample, MU-MIMO may be performed by choosing quasi-orthogonal wirelesscommunication devices 104 in the W₁ matrix 118 domain.

FIG. 2 is a block diagram illustrating a radio network 200 operating inaccordance with the systems and methods disclosed herein. The network200 may include one or more wireless communication devices 204 and oneor more base stations 202. The wireless communication device 204 mayoperate in accordance with the wireless communication device 104described in connection with FIG. 1. Furthermore, the base station 202may operate in accordance with the base station 102 described inconnection with FIG. 1.

In one configuration, the wireless communication device 204 may includea CSI report transmit module 206. The CSI report transmit module maycreate a CSI report 232 based on a codebook 208 a. The wirelesscommunication device 204 may send the CSI report 232 in an uplink symbol230 to a base station 202. The wireless communication device 204 maysend the uplink symbol 230 on the uplink 226. In one configuration, theuplink symbol 230 is sent on a physical uplink shared channel (PUSCH) ora physical uplink control channel (PUCCH).

The uplink symbol 230 may include channel state information (CSI) thatmay be used by the base station 202 to schedule wireless transmissions.In one configuration, the uplink symbol 230 may include a channel stateinformation (CSI) report 232. The channel state information (CSI) report232 may include a combination of channel quality indicator (CQI)information 238, precoding matrix indicator (PMI) information 236 andrank indicator (RI) information 234.

The rank indicator (RI) 234 may indicate the number of layers that canbe supported on a channel (e.g., the number of layers that the wirelesscommunication device 204 can distinguish). Spatial multiplexing (in aMIMO transmission, for example) can be supported only when the rankindicator (RI) 234 is greater than 1. The precoding matrix indicator(PMI) 236 may indicate a precoder out of a codebook 208 (e.g.,pre-agreed parameters) that the base station 202 may use for datatransmission over multiple antennas based on the evaluation by thewireless communication device 204 of a received reference signal.

The codebook 208 may instruct the base station 202 on how to interpret areceived CSI report 232, including what information is included in theCSI report 232 and the formatting of the CSI report 232. For example,the CSI report module 206 may determine a codebook 208 a for the CSIreport 232 corresponding to four transmit antenna (4Tx) transmissionsfrom a base station 202. In one configuration, the codebook 208 a mayhave a dual codebook structure. The codebook 208 a structure may be ablock-diagonal grid of beams (GoB) structure, as described in connectionwith FIG. 1.

The CSI report module 206 may adapt the codebook 208 based on one ormore parameters. For example, the CSI report module 206 may adapt thecodebook 208 based on GoB resolution 110, the size of the beam groups112, the overlap between beam groups 114 and/or the co-phasing accuracy116. The codebook adaptation may be performed to balance the accuracyand feedback overhead of the CSI report 232.

The base station 202 may include a CSI report decode module 222. Thebase station 202 may receive the CSI report 232. The CSI report decodemodule 222 may determine the codebook 208 used to generate the CSIreport 232. The base station 202 may decode the CSI report 232 based onthe codebook 208 b.

FIG. 3 is a flow diagram of a method 300 for CSI reporting usingcodebook adaptation. The method 300 may be performed by a wirelesscommunication device 104. In one configuration, the wirelesscommunication device 104 may provide CSI reports 132 that correspond to4Tx downlink 124 transmissions from a base station 102 to the wirelesscommunication device 104. Codebook adaptation may allow the wirelesscommunication device 104 to use one or more codebooks 108.

The wireless communication device 104 may determine 302 a codebook 108for a CSI report 132. In one configuration, the codebook 108 may have adual codebook structure. For example, the codebook 108 may have ablock-diagonal grid of beams (GoB) structure. A first matrix (e.g., theW1 matrix 118) may define a grid of beams for each polarization. Asecond matrix (e.g., the W2 matrix 120) may perform beam selectionwithin a beam group and co-phasing.

The codebooks 108 used by the wireless communication device 104 may bepredefined. For example, the wireless communication device 104 mayinclude two or more codebooks 108, along with the parameters associatedwith each codebook 108. The codebooks 108 used by the wirelesscommunication device 104 may instead be adaptable. Thus, the wirelesscommunication device 104 may adjust any of the parameters of a codebook108 to obtain an adapted codebook 108. The parameters of a codebook 108may include the GoB resolution 110, the size of the beam groups 112, theoverlap between beam groups 114 and/or the co-phasing accuracy 116. Eachof the parameters may be individually adaptable to form the codebook108.

As discussed above, the wireless communication device 104 mayautonomously select the codebook 108. Alternatively, the wirelesscommunication device 104 may receive signaling from the base station 102on which codebook 108 to select. In one configuration, the wirelesscommunication device 104 may use multiple codebooks 108 for multiple CSIreports 132 and the base station 102 may indicate to the wirelesscommunication device 104 which codebook 108 provides the most benefit.The codebook 108 may be signaled using signaling based on explicit bits,dynamic parameters and/or semi-static parameters.

The wireless communication device 104 may generate 304 the CSI report132 using the codebook 108. The wireless communication device 104 maythen transmit 306 the CSI report 132 to a base station 102.

FIG. 4 is a flow diagram of a method 400 for obtaining CSI reportingusing codebook adaptation. The method 400 may be performed by a basestation 102. In one configuration, the base station 102 may use 4Txdownlink 124 transmissions to a wireless communication device 104.

The base station 102 may determine 402 a codebook 108 used by thewireless communication device 104 for a CSI report 132. In oneconfiguration, the codebook 108 may have a dual codebook structure. Forexample, the codebook 108 may have a block-diagonal grid of beams (GoB)structure. A first matrix (e.g., the W1 matrix 118) may define a grid ofbeams for each polarization. A second matrix (e.g., the W2 matrix 120)may perform beam selection within a beam group and co-phasing.

The codebooks 108 used by the wireless communication device 104 may bepredefined. For example, the wireless communication device 104 mayinclude two or more codebooks 108, along with the parameters associatedwith each codebook 108. The codebooks 108 used by the wirelesscommunication device 104 may instead be adaptable. Thus, the wirelesscommunication device 104 may adjust any of the parameters of a codebook108 to obtain an adapted codebook 108. The parameters of a codebook 108may include the GoB resolution 110, the size of the beam groups 112, theoverlap between beam groups 114 and/or the co-phasing accuracy 116. Eachof the parameters may be individually adaptable to form the codebook108.

As discussed above, the base station 102 may instruct the wirelesscommunication device 104 on which codebook 108 to use (or the parametersof a codebook 108 to use). Alternatively, the base station 102 mayreceive an indication from the wireless communication device 104 ofwhich codebook 108 was used.

The base station 102 may receive 404 the CSI report 132. The CSI report132 may be received before or after the codebook 108 is determined. TheCSI report 132 may include indices corresponding to the first matrix(e.g., W₁ matrix 118) and the second matrix (e.g., W₂ matrix 120),respectively.

The base station 102 may decode 406 the CSI report 132 using thecodebook 108. In one configuration, decoding 406 the CSI report 132using the codebook 108 may include determining which decoder to use todecode the CSI report 132. The base station 102 may use the decoded CSIreport 132 to schedule future downlink 124 transmission to the wirelesscommunication device 104 (including beamforming).

FIG. 5 is a flow diagram of a method 500 for periodic CSI reportingusing codebook adaptation. The method 500 may be performed by a wirelesscommunication device 104. In one configuration, the wirelesscommunication device 104 may provide 502 periodic CSI reports 132 thatcorrespond to 4Tx downlink 124 transmissions from a base station 102 tothe wireless communication device 104. Codebook adaptation may allow thewireless communication device 104 to use one or more codebooks 108 whengenerating a CSI report 132.

In one configuration of periodic feedback, CSI feedback may be supportedbased on PUCCH reporting modes 1-1 and 2-1 using the enhanced codebook108 described herein. This may be accomplished by building upon thereporting types of 8Tx feedback reporting, which are likewise based on adual codebook structure. However, the issue of codebook subsamplingneeds to be addressed for several of the reporting types in order tomeet the 11 bit payload constraint.

The wireless communication device 104 may use 504 a type 5 report for aPUCCH mode 1-1, submode 1. In this reporting mode, the first PMI isreported together with the RI (RI, first PMI) as a type 5 report. Forthe 8Tx case, codebook subsampling is performed despite the fact thatthe aggregated payload remains below the total of 11 bit. In Rel-10, thesubsampling was motivated by achieving higher transmission reliability.The second PMI and CQI are reported as a Type 2b report, similar to theway that reporting is performed for non-dual codebooks 108. No codebooksubsampling is needed for this case.

For the enhanced 4Tx codebook 108 described herein, codebook subsamplingmay be performed for the type 5 (RI, first PMI) report. It may bebeneficial to avoid codebook subsampling as much as possible and toperform subsampling to the extent that it removes redundant precodersthat result from the dual codebook 108 structure. The presence ofredundant precoders results from the concept of beam groups in whichmultiple subband-level PMIs are fed back assuming a single widebandprecoder. However, this is not relevant for PUCCH mode 1-1, where boththe first and the second PMIs are reported on a wideband basis. Forexample, in one configuration, every second entry of the W₁ codebook 108(e.g., W₁ matrix 118) could be removed to avoid overlap between adjacentbeam groups.

Many codebook 108 configurations may achieve a 3 bit payload for thefirst PMI. For 4Tx CSI reporting, this would lead to a maximum payloadof 4 bits for 2-layer spatial multiplexing and 5 bits for 4-layerspatial multiplexing. These payloads are aligned with the payloads usedfor 8Tx feedback reporting. Payloads for PUCCH 1-1, submode 1, feedbackreporting are provided in Table 3 below.

TABLE 3 Reporting Type 1st PMI RI Total payload Type 5 2-layer spatial 3bit 1 bit 4 bit multiplexing 4-layer spatial 3 bit 2 bit 5 bitmultiplexing

The wireless communication device 104 may use 506 a type 2c report for aPUCCH mode 1-1, submode 2. In this reporting mode, the first PMI, secondPMI, and CQI may be reported together as a type 2c report. Thisreporting mode would be desirable to avoid subsampling to the maximumextent. For rank-1, subsampling is not needed as the combined payload of3+3 bits for the enhanced codebook 108 can still be supported (assumingremoval of redundant precoders, as outlined above). Likewise, for rank-3and rank-4, if the Rel-8 codebook 108 is reused, no subsampling isnecessary.

For rank-2, the payload could be reduced to 3 bits for W₁ and 1 bit forW₂. This codebook subsampling is aligned with the 8Tx design. The 1 bitpayload for W₂ would only perform co-phasing. A payload configurationfor PUCCH 1-1, submode 2, feedback reporting is provided in Table 4.

TABLE 4 Reporting Type 1^(st) PMI 2^(nd) PMI CQI Total Type 2c RI = 1 3bit 3 bit 4 bit 10 bit RI = 2 3 bit 1 bit 7 bit 11 bit 3 ≦ RI ≦ 4 n/a 4bit 7 bit 11 bit

The wireless communication device 104 may use 508 a type 1a report for aPUCCH mode 2-1. In this reporting mode, codebook subsampling may only beneeded for reporting type 1a, which includes subband 2nd PMIinformation, subband CQI information and the subband (SB) label. Asshown in Table 5, codebook subsampling may be performed for the RI=2case, assuming that the Rel-8 codebook 108 is reused for rank-3 andrank-4. The subsampling for this case may be performed by either using a1 bit W₂ similar to the subsampling for PUCCH 1-1, submode 2 or by usinga 2 bit W₂ that allows for some additional beam selection. If the Rel-8codebook 108 is reused for rank-3 and rank-4, no subsampling is neededfor the Type 1a report as there is only a single PMI that can bereported in line with the existing Rel-8 reporting procedures.Furthermore, in this case, only a procedure transaction identity (PTI)=0would be supported for rank-3 and rank-4.

TABLE 5 Reporting Type 2^(nd) PMI CQI SB label Total Type 1a RI = 1 3bit 4 bit 2 bit 9 bit RI = 2 1 or 2 bit 7 bit 2 bit 10 or 11 bit 3 ≦ RI≦ 4 n/a 7 bit 2 bit 9 bit

In some cases, periodic CSI feedback reporting necessitates codebooksubsampling to ensure that the total CSI report 132 (e.g., RI/PMI/CQI)payload does not exceed a total of 11 bits. The ability to select a beamcorresponding to any beam direction after performing subsampling shouldbe considered. For the 8Tx codebook, where adjacent W₁ codebook entriesoverlap by 2 beams, subsampling may be accomplished by retaining onlyevery second codebook index. As Table 6 shows, doing so only removes theoverlap between beam groups. Table 6 provides beam group composition forcodebook types 2a/2b vs. the 8Tx codebook.

TABLE 6 W₁ codebook index i1 Scheme 0 1 2 3 4 5 6 7 8 9 10 11 12 13 1415 Codebooks 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 2a/2b 8 9 10 11 12 1314 15 16 17 18 19 20 21 22 23 16 17 18 19 20 21 22 23 24 25 26 27 28 2930 31 24 25 26 27 28 29 30 31 0 1 2 3 4 5 6 7 8Tx 0 2 4 6 8 10 12 14 1618 20 22 24 26 28 30 codebook 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 312 4 6 8 10 12 14 16 18 20 22 24 26 28 30 0 3 5 7 9 11 13 15 17 19 21 2325 27 29 31 1

With the enhanced codebook 108 (e.g., Codebooks 2a/2b) shown in Table 6,adjacent W₁ codebook entries do not overlap by 2 beams. Therefore,selecting every second codebook entry may not allow for the selection ofcertain beam directions. However, selecting the first half of codebookentries preserves the possibility of selecting any of the 32 beams inthe codebook. This may motivate a different subsampling compared to the8Tx codebook.

For codebook subsampling for PUCCH mode 1-1, submode 1, W₁ may bereported together with the RI as a type 5 report, as described above.For the 8Tx case, codebook subsampling may be performed to removeredundant precoders from the W₁ codebook. A similar approach may beperformed for the enhanced codebook 108 as well, although differences inthe W₂ codebook (i.e., the α-offsets) may lead to different overallprecoders between beam groups that contain the same set of beams butwith a different ordering (e.g., entries 0 and 8 in Table 6). The αfactor may allow for a finer co-phasing granularity that is jointlyencoded with the beam selection.

It may be beneficial to avoid codebook subsampling as much as possible.However, codebook subsampling may be considered to the extent thatcodebook subsampling removes beam groups with the same set of beams.This is illustrated in Table 7, which shows that the beam groupsassociated with first PMI index i1 and index i1+8 include the samebeams, though not in the same order.

TABLE 7 W₁ codebook index i1 Scheme 0 1 2 3 4 5 6 7 8 9 10 11 12 13 1415 Beams 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 per beam 8 9 10 11 12 1314 15 16 17 18 19 20 21 22 23 group 16 17 18 19 20 21 22 23 24 25 26 2728 29 30 31 24 25 26 27 28 29 30 31 0 1 2 3 4 5 6 7

In one configuration, the codebook entries in Table 7 for the beams perbeam group corresponding to W₁ codebook index i1 0-7 may be selected,while the codebook entries for the beams per beam group corresponding toW₁ codebook index i1 8-15 may be pruned.

Alternatively, to avoid subsampling and fully use the enhanced codebook108, codebook subset restriction may be employed in animplementation-specific way to achieve the benefit of improvedreliability when needed. In some configurations, codebook subsetrestriction may provide a way for a base station 102 to restrict the setof codebooks 108 and/or ranks that the wireless communication device 104can assume for CSI feedback. While codebook subset restriction does notreduce the transmission payload itself, codebook subset restrictionleads to known bits at the network when decoding the CSI report 132 of awireless communication device 104. This knowledge of a subset of bitscan be exploited in the decoding process to detect the report morereliably.

For codebook subsampling for PUCCH mode 1-1, submode 2, W₁ and W₂ may bereported together as a Type 2c report. Subsampling may be unavoidable inthis case, but it may be desirable to limit the amount of subsampling asmuch as possible. Due to the increased CQI payload for ranks larger thanone, the subsampling may depend on the transmission rank.

For rank-1, 7 bits are available for carrying PMI (4 bits are needed forthe CQI). A total of 3 bits may be allocated to W₁ by removing duplicatebeam groups as shown in Table 7. The remaining 4 bits may be used forfeeding back W₂ without further subsampling.

For rank-2, 4 bits are available for carrying PMI (7 bits are needed forCQI and differential CQI). These 4 bits may be allocated according totwo options. In a first option, 2 bits may be allocated to W₁, whichallows the selection of beam groups as shown in the upper half of Table8. The remaining 2 bits may be allocated to W₂. 1 of the 2 remainingbits allocated to W₂ may select either the first or third beam in thebeam group, and the other bit selects the co-phasing (e.g., either ‘0’or ‘−1’). Table 8 illustrates two options for codebook subsampling forPUCCH 1-1, submode 2, reporting type 2c.

TABLE 8 W₁ codebook index i1 Scheme 0 1 2 3 4 5 6 7 8 9 10 11 12 13 1415 Opt-1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 8 9 10 11 12 13 14 15 1617 18 19 20 21 22 23 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 2425 26 27 28 29 30 31 0 1 2 3 4 5 6 7 Opt-2 0 1 2 3 4 5 6 7 8 9 10 11 1213 14 15 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 16 17 18 19 20 2122 23 24 25 26 27 28 29 30 31 24 25 26 27 28 29 30 31 0 1 2 3 4 5 6 7

In one configuration, the underlined codebook entries in Table 8 denoteselected codebook entries. The remaining codebook entries in Table 8(e.g., non-underlined codebook entries) denote pruned codebook entries.

In a second option, 3 bits may be allocated to W₁, which allowsselecting the beam groups as shown in the bottom half of Table 8. Theremaining 1 bit may be used to perform beam selection of either thefirst or third beam in the beam group. No co-phasing selection isperformed with this option.

The above configurations for codebook subsampling for PUCCH mode 1-1,submode 2 ensure that the codebook is uniformly subsampled across the 32beams contained in the codebook.

For codebook subsampling for PUCCH mode 2-1, codebook subsampling isonly required for reporting type 1a, which includes subband W₂, subbandCQI and the subband selection label. The subsampling may depend on therank. For rank-1, subsampling can be avoided entirely due to thecomparatively smaller CQI payload (as in the case for 8Tx feedbackreporting).

For rank-2, 2 bits are available to carry the W₂ PMI payload. Similar to8Tx feedback reporting, two bits may be used for conveying the beamselection information. For example, the subsampling scheme may selectthe pairs (e₁,e₁), (e₂,e₂), (e₃,e₃), and (e₄,e₄), all with the firstco-phasing option of Equation (1).

$\begin{matrix}{{W_{2,n} \in {\left\{ {{\frac{1}{2}\begin{bmatrix}Y_{1} & Y_{2} \\Y_{1} & {- Y_{2}}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}Y_{1} & Y_{2} \\{jY}_{1} & {- {jY}_{2}}\end{bmatrix}}} \right\} \mspace{14mu} {{and}\left( {Y_{1},Y_{2}} \right)}}} = {\left( {e_{i},e_{k}} \right) \in \left\{ {\left( {e_{1},e_{1}} \right),\left( {e_{2},e_{2}} \right),\left( {e_{3},e_{3}} \right),\left( {e_{4},e_{4}} \right)} \right\}}} & (1)\end{matrix}$

In Equation (1), the e term represents a beam in a beam group in W₁. Forexample, if there are four beams in a beam group in W₁, the four beamscan be represented by e₁, e₂, e₃, and e₄.

For ranks-3 and 4, the 4Tx codebook 108 may reuse the Rel-8 codewordsfor ranks-3 and 4. As for ranks-1 and 2, the PMI payload needs to bereduced from 4 bits to 2 bits. The Rel-8 4Tx codebook 108 includesseveral groups of codewords that target different antennaconfigurations. As a focus of the enhanced codebook 108 is on across-polarized antenna configuration, the codewords that are alignedwith this antenna configuration may be retained in the Rel-8 codebook108. In particular, the last 4 entries in the 4Tx codebook 108 (i.e.,entries 12-15), which correspond to this antenna configuration, may beretained for PUCCH 2-1 reporting.

FIG. 6 is a block diagram of a transmitter 650 and receiver 652 in aMIMO system 600. In some implementations, the transmitter 650 may beimplemented in one or more of the base stations 102. In someimplementations, the receiver 652 may be implemented in one or more ofthe wireless communication devices 104 and base station 102. In thetransmitter 650, traffic data for a number of data streams is providedfrom a data source 654 to a transmit (TX) data processor 656. Each datastream may then be transmitted over a respective transmit antenna 658a-t. The transmit (TX) data processor 656 may format, code, andinterleave the traffic data for each data stream based on a particularcoding scheme selected for that data stream to provide coded data.

The coded data for each data stream may be multiplexed with pilot data(e.g., reference signals) using orthogonal frequency-divisionmultiplexing (OFDM) techniques. The pilot data may be a known datapattern that is processed in a known manner and used at the receiver 652to estimate the channel response. The multiplexed pilot and coded datafor each stream is then modulated (i.e., symbol mapped) based on aparticular modulation scheme (e.g., binary phase shift keying (BPSK),quadrature phase shift keying (QPSK), multiple phase shift keying(M-PSK) or multi-level quadrature amplitude modulation (M-QAM)) selectedfor that data stream to provide modulation symbols. The data rate,coding and modulation for each data stream may be determined byinstructions performed by a processor.

The modulation symbols for all data streams may be provided to atransmit (TX) multiple-input multiple-output (MIMO) processor 660, whichmay further process the modulation symbols (e.g., for OFDM). Thetransmit (TX) multiple-input multiple-output (MIMO) processor 660 thenprovides NT modulation symbol streams to NT transmitters (TMTR) 662 athrough 662 t. The TX transmit (TX) multiple-input multiple-output(MIMO) processor 660 may apply beamforming weights to the symbols of thedata streams and to the antenna 658 from which the symbol is beingtransmitted.

Each transmitter 662 may receive and process a respective symbol streamto provide one or more analog signals, and further condition (e.g.,amplify, filter, and upconvert) the analog signals to provide amodulated signal suitable for transmission over the MIMO channel. NTmodulated signals from transmitters 662 a through 662 t are thentransmitted from NT antennas 658 a through 658 t, respectively.

At the receiver 652, the transmitted modulated signals are received byNR antennas 664 a through 664 r, and the received signal from eachantenna 664 is provided to a respective receiver (RCVR) 666 a through666 r. Each receiver 666 may condition (e.g., filter, amplify, anddownconvert) a respective received signal, digitize the conditionedsignal to provide samples, and further process the samples to provide acorresponding “received” symbol stream.

An RX data processor 668 then receives and processes the NR receivedsymbol streams from NR receivers 666 based on a particular receiverprocessing technique to provide NT “detected” symbol streams. The RXdata processor 668 then demodulates, deinterleaves and decodes eachdetected symbol stream to recover the traffic data for the data stream.The processing by RX data processor 668 may be complementary to thatperformed by TX MIMO processor 660 and TX data processor 656 attransmitter system 650.

A processor 670 may periodically determine which pre-coding matrix touse. The processor 670 may store information on and retrieve informationfrom memory 672. The processor 670 formulates a reverse link messagecomprising a matrix index portion and a rank value portion. The reverselink message may be referred to as channel state information (CSI). Thereverse link message may comprise various types of information regardingthe communication link and/or the received data stream. The reverse linkmessage is then processed by a TX data processor 674, which alsoreceives traffic data for a number of data streams from a data source676, modulated by a modulator 678, conditioned by transmitters 666 athrough 666 r, and transmitted back to the transmitter 650.

At the transmitter 650, the modulated signals from the receiver arereceived by antennas 658, conditioned by receivers 662, demodulated by ademodulator 680 and processed by an RX data processor 682 to extract thereverse link message transmitted by the receiver system 652. A processor684 may receive channel state information (CSI) from the RX dataprocessor 682. The processor 684 may store information on and retrieveinformation from memory 686. The processor 684 then determines whichpre-coding matrix to use for determining the beamforming weights andthen processes the extracted message.

FIG. 7 illustrates certain components that may be included within awireless communication device 704. The wireless communication device 704may be an access terminal, a mobile station, a user equipment (UE), etc.The wireless communication device 704 includes a processor 703. Theprocessor 703 may be a general purpose single- or multi-chipmicroprocessor (e.g., an Advanced RISC (Reduced Instruction SetComputer) Machine (ARM)), a special purpose microprocessor (e.g., adigital signal processor (DSP)), a microcontroller, a programmable gatearray, etc. The processor 703 may be referred to as a central processingunit (CPU). Although just a single processor 703 is shown in thewireless communication device 704 of FIG. 7, in an alternativeconfiguration, a combination of processors (e.g., an ARM and DSP) couldbe used.

The wireless communication device 704 also includes memory 705. Thememory 705 may be any electronic component capable of storing electronicinformation. The memory 705 may be embodied as random access memory(RAM), read-only memory (ROM), magnetic disk storage media, opticalstorage media, flash memory devices in RAM, on-board memory includedwith the processor, erasable programmable read-only memory (EPROM),electrically erasable programmable read-only memory (EEPROM) memory,registers, and so forth, including combinations thereof.

Data 707 a and instructions 709 a may be stored in the memory 705. Theinstructions 709 a may be executable by the processor 703 to implementthe methods disclosed herein. Executing the instructions 709 a mayinvolve the use of the data 707 a that is stored in the memory 705. Whenthe processor 703 executes the instructions 709 a, various portions ofthe instructions 709 b may be loaded onto the processor 703, and variouspieces of data 707 b may be loaded onto the processor 703.

The wireless communication device 704 may also include a transmitter 711and a receiver 713 to allow transmission and reception of signals to andfrom the wireless communication device 704. The transmitter 711 andreceiver 713 may be collectively referred to as a transceiver 715. Anantenna 717 may be electrically coupled to the transceiver 715. Thewireless communication device 704 may also include (not shown) multipletransmitters, multiple receivers, multiple transceivers and/oradditional antennas.

The wireless communication device 704 may include a digital signalprocessor (DSP) 721. The wireless communication device 704 may alsoinclude a communications interface 723. The communications interface 723may allow a user to interact with the wireless communication device 704.

The various components of the wireless communication device 704 may becoupled together by one or more buses, which may include a power bus, acontrol signal bus, a status signal bus, a data bus, etc. For the sakeof clarity, the various buses are illustrated in FIG. 7 as a bus system719.

FIG. 8 illustrates certain components that may be included within a basestation 802. A base station 802 may also be referred to as, and mayinclude some or all of the functionality of, an access point, abroadcast transmitter, a NodeB, an evolved NodeB, etc. The base station802 includes a processor 803. The processor 803 may be a general purposesingle- or multi-chip microprocessor (e.g., an ARM), a special purposemicroprocessor (e.g., a digital signal processor (DSP)), amicrocontroller, a programmable gate array, etc. The processor 803 maybe referred to as a central processing unit (CPU). Although just asingle processor 803 is shown in the base station 802 of FIG. 8, in analternative configuration, a combination of processors (e.g., an ARM andDSP) could be used.

The base station 802 also includes memory 805. The memory 805 may be anyelectronic component capable of storing electronic information. Thememory 805 may be embodied as random access memory (RAM), read-onlymemory (ROM), magnetic disk storage media, optical storage media, flashmemory devices in RAM, on-board memory included with the processor,EPROM, EEPROM, registers and so forth, including combinations thereof.

Data 807 a and instructions 809 a may be stored in the memory 805. Theinstructions 809 a may be executable by the processor 803 to implementthe methods disclosed herein. Executing the instructions 809 a mayinvolve the use of the data 807 a that is stored in the memory 805. Whenthe processor 803 executes the instructions 809 a, various portions ofthe instructions 809 b may be loaded onto the processor 803, and variouspieces of data 807 b may be loaded onto the processor 803.

The base station 802 may also include a transmitter 811 and a receiver813 to allow transmission and reception of signals to and from the basestation 802. The transmitter 811 and receiver 813 may be collectivelyreferred to as a transceiver 815. An antenna 817 may be electricallycoupled to the transceiver 815. The base station 802 may also include(not shown) multiple transmitters, multiple receivers, multipletransceivers and/or additional antennas.

The base station 802 may include a digital signal processor (DSP) 821.The base station 802 may also include a communications interface 823.The communications interface 823 may allow a user to interact with thebase station 802.

The various components of the base station 802 may be coupled togetherby one or more buses, which may include a power bus, a control signalbus, a status signal bus, a data bus, etc. For the sake of clarity, thevarious buses are illustrated in FIG. 8 as a bus system 819.

The techniques described herein may be used for various communicationsystems, including communication systems that are based on an orthogonalmultiplexing scheme. Examples of such communication systems includeOrthogonal Frequency Division Multiple Access (OFDMA) systems,Single-Carrier Frequency Division Multiple Access (SC-FDMA) systems, andso forth. An OFDMA system utilizes orthogonal frequency divisionmultiplexing (OFDM), which is a modulation technique that partitions theoverall system bandwidth into multiple orthogonal sub-carriers. Thesesub-carriers may also be called tones, bins, etc. With OFDM, eachsub-carrier may be independently modulated with data. An SC-FDMA systemmay utilize interleaved FDMA (IFDMA) to transmit on sub-carriers thatare distributed across the system bandwidth, localized FDMA (LFDMA) totransmit on a block of adjacent sub-carriers, or enhanced FDMA (EFDMA)to transmit on multiple blocks of adjacent sub-carriers. In general,modulation symbols are sent in the frequency domain with OFDM and in thetime domain with SC-FDMA.

The term “determining” encompasses a wide variety of actions and,therefore, “determining” can include calculating, computing, processing,deriving, investigating, looking up (e.g., looking up in a table, adatabase or another data structure), ascertaining and the like. Also,“determining” can include receiving (e.g., receiving information),accessing (e.g., accessing data in a memory) and the like. Also,“determining” can include resolving, selecting, choosing, establishingand the like.

The phrase “based on” does not mean “based only on,” unless expresslyspecified otherwise. In other words, the phrase “based on” describesboth “based only on” and “based at least on.”

The term “processor” should be interpreted broadly to encompass ageneral purpose processor, a central processing unit (CPU), amicroprocessor, a digital signal processor (DSP), a controller, amicrocontroller, a state machine, and so forth. Under somecircumstances, a “processor” may refer to an application specificintegrated circuit (ASIC), a programmable logic device (PLD), a fieldprogrammable gate array (FPGA), etc. The term “processor” may refer to acombination of processing devices, e.g., a combination of a DSP and amicroprocessor, a plurality of microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration.

The term “memory” should be interpreted broadly to encompass anyelectronic component capable of storing electronic information. The termmemory may refer to various types of processor-readable media such asrandom access memory (RAM), read-only memory (ROM), non-volatile randomaccess memory (NVRAM), programmable read-only memory (PROM), erasableprogrammable read-only memory (EPROM), electrically erasable PROM(EEPROM), flash memory, magnetic or optical data storage, registers,etc. Memory is said to be in electronic communication with a processorif the processor can read information from and/or write information tothe memory. Memory that is integral to a processor is in electroniccommunication with the processor.

The terms “instructions” and “code” should be interpreted broadly toinclude any type of computer-readable statement(s). For example, theterms “instructions” and “code” may refer to one or more programs,routines, sub-routines, functions, procedures, etc. “Instructions” and“code” may comprise a single computer-readable statement or manycomputer-readable statements.

The functions described herein may be implemented in software orfirmware being executed by hardware. The functions may be stored as oneor more instructions on a computer-readable medium. The terms“computer-readable medium” or “computer-program product” refers to anytangible storage medium that can be accessed by a computer or aprocessor. By way of example, and not limitation, a computer-readablemedium may comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage or other magnetic storage devices, or anyother medium that can be used to carry or store desired program code inthe form of instructions or data structures and that can be accessed bya computer. Disk and disc, as used herein, includes compact disc (CD),laser disc, optical disc, digital versatile disc (DVD), floppy disk andBlu-Ray® disc where disks usually reproduce data magnetically, whilediscs reproduce data optically with lasers. It should be noted that acomputer-readable medium may be tangible and non-transitory. The term“computer-program product” refers to a computing device or processor incombination with code or instructions (e.g., a “program”) that may beexecuted, processed or computed by the computing device or processor. Asused herein, the term “code” may refer to software, instructions, codeor data that is/are executable by a computing device or processor.

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isrequired for proper operation of the method that is being described, theorder and/or use of specific steps and/or actions may be modifiedwithout departing from the scope of the claims.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein, suchas those illustrated by FIGS. 3, 4 and 5 can be downloaded and/orotherwise obtained by a device. For example, a device may be coupled toa server to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via a storage means (e.g., random access memory (RAM),read-only memory (ROM), a physical storage medium such as a compact disc(CD) or floppy disk, etc.), such that a device may obtain the variousmethods upon coupling or providing the storage means to the device.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the systems, methods, and apparatus described herein withoutdeparting from the scope of the claims.

What is claimed is:
 1. A method for channel state information (CSI)reporting, comprising: determining, by a wireless communication device,a codebook for a CSI report corresponding to four transmit antenna (4Tx)transmissions from a base station, wherein the codebook has a dualcodebook structure comprising a block-diagonal grid of beams structureW=W₁·W₂, wherein W₁ is a first matrix that is reported on a widebandbasis, wherein W₂ is a second matrix that is reported on a subbandbasis; generating, by the wireless communication device, the CSI reportusing the codebook; and transmitting, by the wireless communicationdevice, the CSI report to a base station.
 2. The method of claim 1,wherein the first matrix (W₁) defines a grid of beams for eachpolarization, and wherein the second matrix (W₂) performs beam selectionwithin a beam group and co-phasing.
 3. The method of claim 1, whereinthe codebook is determined based on at least one of a grid of beamresolution, a size of beam groups, an overlap between beam groups, and aco-phasing accuracy.
 4. The method of claim 3, wherein each parameterused to generate the codebook is individually adaptable.
 5. The methodof claim 1, further comprising signaling the codebook using signalingbased on at least one of explicit bits, dynamic parameters andsemi-static parameters.
 6. The method of claim 1, wherein new reportingtypes are defined to adjust the number of bits spent for a precodingmatrix indicator (PMI) or a channel quality indicator (CQI) in variousreporting modes.
 7. The method of claim 1, wherein the wirelesscommunication device determines which of multiple configured codebooksshould be used for CSI reporting.
 8. The method of claim 1, whereinmultiple user channel quality indicator hypotheses remain separate fromcodebook adaptation.
 9. The method of claim 1, wherein multiple userchannel quality indicator hypotheses follow codebook adaptation.
 10. Themethod of claim 1, further comprising performing codebook subsampling tomeet an 11 bit payload constraint for the CSI report.
 11. A wirelesscommunication device for channel state information (CSI) reporting,comprising: a processor; memory in electronic communication with theprocessor; and instructions stored in the memory, the instructions beingexecutable by the processor to: determine, by the wireless communicationdevice, a codebook for a CSI report corresponding to four transmitantenna (4Tx) transmissions from a base station, wherein the codebookhas a dual codebook structure comprising a block-diagonal grid of beamsstructure W=W₁·W₂, wherein W₁ is a first matrix that is reported on awideband basis, wherein W₂ is a second matrix that is reported on asubband basis; generate, by the wireless communication device, the CSIreport using the codebook; and transmit, by the wireless communicationdevice, the CSI report to a base station.
 12. The wireless communicationdevice of claim 11, wherein the first matrix (W₁) defines a grid ofbeams for each polarization, and wherein the second matrix (W₂) performsbeam selection within a beam group and co-phasing.
 13. The wirelesscommunication device of claim 11, wherein the codebook is determinedbased on at least one of a grid of beam resolution, a size of beamgroups, an overlap between beam groups, and a co-phasing accuracy. 14.The wireless communication device of claim 13, wherein each parameterused to generate the codebook is individually adaptable.
 15. Thewireless communication device of claim 11, further comprisinginstructions being executable by the processor to signal the codebookusing signaling based on at least one of explicit bits, dynamicparameters and semi-static parameters.
 16. The wireless communicationdevice of claim 11, wherein new reporting types are defined to adjustthe number of bits spent for a precoding matrix indicator (PMI) or achannel quality indicator (CQI) in various reporting modes.
 17. Thewireless communication device of claim 11, wherein the wirelesscommunication device determines which of multiple configured codebooksshould be used for CSI reporting.
 18. The wireless communication deviceof claim 11, wherein multiple user channel quality indicator hypothesesremain separate from codebook adaptation.
 19. The wireless communicationdevice of claim 11, wherein multiple user channel quality indicatorhypotheses follow codebook adaptation.
 20. The wireless communicationdevice of claim 11, further comprising instructions being executable bythe processor to perform codebook subsampling to meet an 11 bit payloadconstraint for the CSI report.
 21. A wireless communication device forchannel state information (CSI) reporting, comprising: means fordetermining a codebook for a CSI report corresponding to four transmitantenna (4Tx) transmissions from a base station, wherein the codebookhas a dual codebook structure comprising a block-diagonal grid of beamsstructure W=W₁·W₂, wherein W₁ is a first matrix that is reported on awideband basis, wherein W₂ is a second matrix that is reported on asubband basis; means for generating the CSI report using the codebook;and means for transmitting the CSI report to a base station.
 22. Thewireless communication device of claim 21, wherein the codebook isdetermined based on at least one of a grid of beam resolution, a size ofbeam groups, an overlap between beam groups, and a co-phasing accuracy.23. The wireless communication device of claim 22, wherein eachparameter is individually adaptable to form the codebook.
 24. Thewireless communication device of claim 21, further comprising means forsignaling the codebook using signaling based on at least one of explicitbits, dynamic parameters and semi-static parameters.
 25. The wirelesscommunication device of claim 21, further comprising means fordetermining which of multiple configured codebooks should be used forCSI reporting.
 26. A computer-program product for channel stateinformation (CSI) reporting, the computer-program product comprising anon-transitory computer-readable medium having instructions thereon, theinstructions comprising: code for causing a wireless communicationdevice to determine a codebook for a CSI report corresponding to fourtransmit antenna (4Tx) transmissions from a base station, wherein thecodebook has a dual codebook structure comprising a block-diagonal gridof beams structure W=W₁·W₂, wherein W₁ is a first matrix that isreported on a wideband basis, wherein W₂ is a second matrix that isreported on a subband basis; code for causing the wireless communicationdevice to generate the CSI report using the codebook; and code forcausing the wireless communication device to transmit the CSI report toa base station.
 27. The computer-program product of claim 26, whereinthe codebook is determined based on at least one of a grid of beamresolution, a size of beam groups, an overlap between beam groups, and aco-phasing accuracy.
 28. The computer-program product of claim 27,wherein each parameter is individually adaptable to form the codebook.29. The computer-program product of claim 26, further comprising codefor causing the wireless communication device to signal the codebookusing signaling based on at least one of explicit bits, dynamicparameters and semi-static parameters.
 30. The computer-program productof claim 26, further comprising code for causing the wirelesscommunication device to determine which of multiple configured codebooksshould be used for CSI reporting.